Hi Debs,
Not 100% sure as I am no doctor but I think the white matter is the area left on the brain after the stroke has occured, basically "killing" off the brain cells in this particular area.

I would get more information from a neuro to explain this as I am not sure if I am right
Moira

All brains have white matter and grey matter.    I'm not sure what it would mean to have a lot of white matter... I found information about decreased white matter density (can be due to MS or other diseases)  but nothing about increased white matter density.   Anyway, here is a description of white matter that I found online that might help a little:

The White Matter regions of the central nervous system contrast with the Grey Matter regions. The White Matter refers to those parts of the brain and spinal cord that are responsible for communication between the various grey matter regions and between the grey matter and the rest of the body. In essence, the grey matter is where the processing is done and the white matter is the channels of communication.

By analolgy, the grey matter is like the CPU in a computer and the white matter is like the printed circuit board that connects it to the other parts of the computer.

The white matter is so-called because it contains lots of nerve fibres (neurons) that are sheathed in a white fatty insulating protein called myelin. In section, myelin is white whereas the grey matter is grey due to all the grey nuclei in the cells that make it up.

Multiple Sclerosis is predominantly a disease of the white matter in the central nervous system. About 95% of all lesions associated with multiple sclerosis occur in the white matter.

The white matter is found in the inner layer of the cortex, the optic nerves, the central and lower areas of the brain (notably the Brainstem) and surrounding the central shaft of grey matter in the spinal cord.